Occasionally back draft on gas boiler.

ebereit

I've seen a discussion about a back draft with a gas boiler heater. This has been an occasional occurrence. Some things have been eliminated as far as possible causes; not blocked, cleaned within past year, no other appliances contributing. There wasn't a problem like this until a year ago. Again, it's not a frequent occurrence. Any thoughts?

Jamie Hall

What changed about a year ago?

ebereit

The chimneys were cleaned. There is a fireplace in basement that has been closed off, an insert was placed in first floor fireplace, they are separate chimneys far from boiler and coming out of second floor roof.

Bob Harper

The water heater's vent connector is undersized and does not have the maximum vent rise possible or is it supported.

The boiler's vent connector crams in beside the WH so the question is, do they manifold or run co-linear into the wall? There should be one stainless steel vent connector into the flue. I don't see a chimney cleanout within a foot of the base as required. If this is a stainless steel liner then ok. If it is a masonry flue, whether tile lined or not it needs to be relined.

You would need to perform a Worst Case Depressurization Test and survey the house to see what interactions there are.

pecmsg

negative pressure?

ebereit

Water heater was installed 10 years ago. The pitch is the same as original water heater was. Not arguing, just how was. Vents go in separate with no liner. Chimney clean out is outside. I want to have the boiler inspected and like the idea of test done. Preferring some one familiar with this type of equipment.

HVACNUT

Everything those ☝️ guys said, plus, you don't need to oil the gas valve any further.